1. Field of the Invention
This invention relates, generally, to syringes. More particularly, it relates to an attachment that is retrofit to a syringe to enable one hand operation and control of the position of the plunger from a point near a leading end of the syringe.
2. Description of the Prior Art
A conventional syringe structure includes a needle held at its base by a hub that is mounted at the leading end of a barrel. A plunger is slideably mounted in the barrel, and a piston having annular seals is provided at the leading end of the plunger. In a syringe used as an aspirator, withdrawal of the piston/plunger in a leading-to-trailing direction creates a vacuum in the leading end of the barrel that pulls liquid fluid into the barrel. In a syringe used for injection, displacement of the piston/plunger in a trailing-to-leading direction drives a liquid fluid out of the barrel and through the needle into the patient's tissue.
Some syringes are used for aspiration and injection. Thus, the plunger is retracted to accomplish aspiration, and thereafter advanced to accomplish injection. When a conventional syringe is used in this manner, the physician must develop a technique whereby the needle remains properly positioned during the retraction and the advancement of the plunger. The most common way of performing an aspiration is for the operator to hold the barrel in a first hand and to retract the piston/plunger with a second hand. For injection, the operator usually employs a one-handed technique. The operator steadies the barrel by holding two laterally-extending tabs at the trailing end of the barrel with the index and middle fingers and by using the thumb to advance the plunger in a distal-to-proximal (trailing-to-leading) direction in a well-known way.
There are occasions, however, when it is necessary to inject substances in a precise location, such as a vascular space. Any inadvertent injection of the substance outside its intended target may harm the patient. For example, in the practice of sclerotherapy, a caustic substance is injected into superficial, diseased veins to destroy them. The veins may be quite small and thin-walled and they are typically difficult to cannulate precisely with a needle tip. The patient experiences tissue destruction, ulceration and the pain concomitant therewith if the caustic substance is injected into tissue adjacent the diseased vein, so precision injection is a necessity. Accordingly, when performing an intravascular injection, the physician confirms needle tip location in the vascular space by aspiration until blood is seen. This requires retraction of the plunger. Injection, which requires advancement of the plunger, may then proceed.
The syringes now in use require the physician to change hand positions between the aspiration and the injection. Most physicians have developed their own personal techniques for controlling the plunger position with the same hand that holds the barrel of the syringe. These techniques include positioning a little finger on the trailing end of the plunger, holding the barrel in the palm of a hand so that the palm controls the plunger position, and other non-ergonomic techniques. The drawback of these techniques is that they require a high level of skill and cannot be repeated with consistency. Moreover, a change in hand position can lead to an accidental extravascular injection.
A number of syringes suitable for one-handed operation have been patented, but many of them are relatively complex in construction, difficult to use, and expensive to manufacture.
An earlier invention by the present inventor is believed to represent the most pertinent prior art to the present invention. That invention provides a syringe that can be controlled with one hand, but the novel mechanism is formed integrally with the syringe. Therefore, it does not compare favorably in price with conventional syringes because conventional syringes are made in very high quantities and thus are very inexpensive on a per syringe basis.
What is needed, then, is a low cost device that facilitates one-handed control during aspiration and injection that can be retrofit onto an existing syringe. The device should reduce the level of skill required for its use. Moreover, it should have a simple construction, be easy to use, easy to attach to an existing syringe of conventional construction, and should be economical to manufacture.
More particularly, a syringe attachment retrofittable to a conventional syringe is needed that enables sequential aspiration and injection with one hand in the absence of any need to change hand positions or to otherwise place the fingers, thumb or palm in an awkward position. The attachment would enable the operator to control the instantaneous position of the plunger with a single digit such as a thumb or a finger without requiring movement of any other part of the hand. This would provide more stability so that accurate injection into the proper space could be accomplished. The control point should be positioned forwardly, near the needle, to facilitate its use.
However, it was not obvious to those of ordinary skill in this art how the needed syringe could be provided, in view of the art considered as a whole at the time the present invention was made.